Re: A Problem With The Semantics of DAML+OIL Restrictions

(Pat, to Tim B-L:)

> > Obviously,
> > there are cases where one wants to be able to say this, to be able to
> > give necessary and sufficient conditions. We do this when we say two
> > names are equivalent, for example, in effect. But I think your point
> > arises in the form: how can we adopt this open-ended attitude, and
> > state necessary conditions on restrictions *without* saying they are
> > sufficient? That would be easy to characterise semantically, but I
> > suspect might place a burden on a DAML+OIL reasoner which would break
> > decideability.  (? Any DL expert care to comment?)

(Ian:)

>I'm not sure I understand your concern here. If C is an arbitrary
>class and R is a restriction, then In DAML+OIL we can state any or all
>of C -> R, R -> C, or C <-> R (i.e., subClassOf C R, subClassOf R C,
>sameClassAs C R). This does not have an adverse effect on
>decidability, and modern DL reasoners (such as FaCT) can easily cope
>with this.

I'm not sure I understand it either, but the issue is not in saying 
these things for class relationships,  but saying the analogous 
things for restrictions. The answer may be obvious, and if so I 
apologise, but how would I state necessary but not sufficient 
conditions on a restriction, in such a way that further conditions 
could be added monotonically by further statements?

Pat

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